This invention relates to cylinder liners, and in particular to cylinder liners which are designed as wet liners with a mid-stop flange incorporated into the liner.
For convenience in this specification and the accompanying claims, each constituent cylinder liner in an engine block in accordance with the present invention is considered to have an axis of symmetry which extends vertically above a co-operating crankshaft. The end of the liner remote from the crankshaft is referred to as the top or upper end, and the other end (closest to the crankshaft) is referred to as the top lower or bottom end. Approximately from the level of the midstop flange to the upper end of the liner is considered the outer portion of the liner, and the remaining portion from said midstop flange level to the bottom end is considered the inner portion of the liner. However, it will be understood that references describing the relative positions of the ends, and of the two constituent portions, of any arrangement within an engine block of a liner in accordance with the present invention, are included in the corresponding references given above with respect to the arrangement of a liner extending vertically above the crankshaft.
Further, the term radial, or radially-extending, is used in respect of any distance, or feature, extending in any direction in a plane at right angles to the axis of the cylinder liner; and the term axial, or axially-extending, is used in respect of any distance, or feature, extending parallel to the liner axis.
A cylinder liner of the general type to which the present invention relates is described and claimed in UK Patent No 2 035 452. This specification describes a cylinder liner which has, in combination, a series of features which include a top boss on the liner, the top boss having an axially extending cylindrical surface forming an interference fit with the engine block when in position; a midstop flange with a surface which extends radially outwardly from the liner and engages a complementary radially extending ledge in the engine block; an upper portion between the top boss and the midstop flange which forms a wall of a coolant passage, the axial length of which passage wall is not more than 30% of the axial length of the liner; and an inner portion which has an axial length of at least 30% of the axial length of the liner, and which is wholly free of direct supporting and heat conducting contact with the engine block.
In practice this liner design suffers from the disadvantage that lack of radial support at its bottom end allows the inner portion of the liner to ovalise during use to an undesirable extent, and under extreme conditions this is liable to lead to cracking of the liner.
From a practical point of view, however, it is difficult to provide an adequate support at the bottom end of the liner since this end of the liner is to be inserted into the block first, and the liner has an interference fit on the top boss, as stated above.
An object of the present invention is to provide a liner which is able to have adequate radial support at its bottom end, and yet is readily fitted in the engine block.
Thus, according to the present invention there is provided in an internal combustion engine having a block containing a cylinder cavity extending between the engine head and a crankshaft to which a piston is connected for reciprocating travel within the cylinder cavity, a liner stop positioned intermediate the ends of the cylinder cavity, a liner coolant passage formed to provide coolant to the outer surface of the liner, and a substantially annular radial support section for the bottom end of the liner, a substantially cylindrical replaceable cylinder liner having top and bottom ends which comprises:
i) a top end boss having a cylindrical axially extending outer surface forming an interference fit within the cylinder cavity,
(ii) a midstop flange having a radially extending surface which engages the liner stop in the cylinder cavity,
(iii) a portion between the top boss and midstop flange which forms a wall of the coolant passage,
(iv) a substantially cylindrical inner portion below the midstop flange which forms at least 30% of the axial length of the liner,
(v) an annular groove in the outer surface of the liner adjacent to the bottom end of the liner, and
(vi) a support ring located in said groove, the ring having an outside diameter not substantially greater than an outside diameter of the bottom end before use, and a material which will swell under the influence of engine oil to thereby cause the support ring to contact the substantially annular radial support section.
It will be appreciated that at the bottom end of the liner, the support ring is effectively retracted when the liner is fitted, but swells to contact the annular radial support section, to give damping and radial support for the bottom end of the liner when in use in the engine.
The substantially annular radial support section for the bottom end of the liner may be discontinuous if gaps are required through which oil can drain, for example, but it is important that the support section is present at those locations on the block which are opposite to the thrust and non-thrust faces of the liner, that is, in the plane within which a connecting rod will move when it is attached to a piston located in the liner, such plane also being perpendicular to the axis of rotation of the crankshaft of the engine.
If desired, the support ring may be notched or otherwise shaped to ensure that oil can drain past the ring. The preferred material for the support ring is a rubber compound, which is preferably also heat conductive to ensure that the rubber does not form a thermal barrier between the bottom end of the cylinder liner and the annular radial support section of the block. Preferred rubbers are nitrile rubbers, fluoroelastomers such as Viton, which is a copolymer of vinylidene fluoride and hexafluoropropylene, and chloropolymers such as Neoprene, which is 2-chloro-1, 3-butadiene.
The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings.